A related copending application is U.S. Ser. No. 179,109 filed Apr. 8, 1988.
The present invention relates to a method of estimating and compensating motion in a sequence of pictures in which the brightness of each picture element is expressed digitally. It also relates to an arrangement for estimating and compensating motion for putting this method into effect, and also a picture transmission system provided with such an arrangement, and the transmission and receiving stages of such a system. In the sequel of the present description it will be described that this type of motion estimation and compensation applies to a method of sub-sampling and temporal interpolation.
Such an invention is suitable for use in, for example, the field of high-definition television, and also in applications as, for exampe, tele-meetings (also denoted video-conference) or in the recording of pictures. The French Patent Application FR-A 2,590,701 (PHF 85/591); U.S. Pat. No. 4,766,490 describes a motion estimating arrangement which is based on a recursive displacement estimation method. Put more accurately, in this method there occurs, in accordance with a predetermined criterion, a classification of the picture elements into three groups in which these points are classed, with a delay of L elements, in accordance with the progressing scanning of the picture. This classification is effected after examination of a classifying tree whose successive branches correspond to three possible groups to which L consecutive elements are assumed to belong. Optionally, this classification is effected in a simplified manner, after examination, in said tree, of a predetermined, limited number of these possible sequences of groups for the L picture elements subsequent to the present considered element.
When, in a sequence of picture one wants to recover a picture on the basis of the preceding picture, the arrangement described in said document thus indeed operates satisfactorily. The operating principle of this arrangement has however proved to be not suitable when it is used in high-definition television. In that application, an additional processing operation has indeed proved to be necessary to adapt to the transmission channel (the analog channel provided when the MAC-packet transmission standard is used which is called-on to replace the SECAM and PAL standards) the very large quantity of information components to be transmitted. Such a processing operation may, among other examples, comprise a spatial sub-sampling operation which has for its effect to regularly suppress a certain number of picture elements within the same picture or within the same field, or in a temporal sub-sampling operation which has for its effect to suppress regularly a certain number of pictures or fields in a sequence of pictures.
In high-definition television, this periodical cancellation of a certain number of pictures or fields, for example one picture out of every two pictures, compels a recovery on the basis of the picture of rank n-2, which is located further on. This recovery would be possible but does not allow the recovery of the appropriate quality of a high-definition picture.